In the fabrication process for semiconductor devices, numerous fabrication steps, as many as several hundred, must be executed on a silicon wafer in order to complete integrated circuits on the wafer. Since the processing of silicon wafers requires extreme cleanliness in the processing environment to minimize the presence of contaminating particles or films, the surface of the silicon wafer is frequently cleaned after each processing step. For instance, the wafer surface is cleaned after the deposition of a surface coating layer such as oxide or metal. A frequently-used method for cleaning the wafer surface is a wet-scrubbing method.
In cleaning a wafer surface by a wet scrubbing method, a wafer is rotated at a high speed, i.e., at least about 200 RPM and preferably, about 1,000 RPM, simultaneously with a jet of high-pressure de-ionized water sprayed on top or back surface. The water jet is normally sprayed at a pressure of about 5 to about 10 MPA. The water movement on top of the wafer surface displaces any contaminating particles that are lodged on the wafer surface.
A cleaning process is widely used after a deposition step. The fell-on particle (particle on deposition surface) after deposition such as metal or oxide layer deposition can be removed by a jet scrubbing method. By using high-pressured de-ionized water, the particle on a flat film (deposition surface) will be easily removed.
The pressure of de-ionized water can be controlled to maintain a particle removal rate by adjusting a jet pump pressure. The higher pressure achieves a better particle removal rate. On the other hand, higher pressure may induce damage on a wafer surface. A limitation pressure is set up to avoid this situation. In order to improve a particle removal rate, extending the process time is the only way to achieve such a goal. Although extending the process time will increase the production duration. A novel jet clean nozzle having multiple spray openings is introduced to provide a high particle removal rate and efficient productivity.
FIG. 1 illustrates a silicon wafer 10 the upper surface of which is scanned in a water jet scrubbing method using a conventional wafer scrubbing apparatus 8. The wafer 10 is normally positioned on a wafer platform 17 which is typically rotatably mounted on a wafer stage 16. The wafer platform 17 rotates the wafer 10 at a predetermined rotational speed, which may be between typically about 200 RPM and about 2,000 RPM.
The wafer scrubbing apparatus 8 typically includes a nozzle adaptor 26 which is mounted on a support rack 28. A nozzle 30, having a single nozzle opening 32, is provided on the nozzle adaptor 26, as shown in FIG. 1A. A jet pump (not shown) is connected to an inlet end 27 of the nozzle adaptor 26 to pump water through the nozzle adaptor 26 and nozzle 30. A water jet 22 of de-ionized water is ejected onto the upper surface of the wafer 10 from the single nozzle opening 32 of the nozzle 30. The water jet 22 has a water pressure of typically about 50 kg/cm2.
As it strikes the surface of the wafer 10 at an angle of typically about 45°, the water jet 22 is scanned along a top of the wafer surface by a lateral sweeping motion of the water jet nozzle 26 to define a generally curved or arcuate trace 12 which normally traverses the center 14 of the wafer 10, as illustrated in FIG. 2. The surface of the wafer 10 is scanned by the water jet 22 at least once, and preferably, several times. Centrifugal force acting on the water flow on the surface of the wafer 10 due to the rotating wafer platform 17 and wafer 10 removes contaminating particles or films from the surface of the wafer 10.
It has been found that horizontal movement of the wafer stage beneath the water jet nozzle during the scrubbing process provides a more uniform dispersement of the sprayed water along the entire surface of the disc. This has been found to substantially improve removal of organic particles from the wafer which would otherwise tend to remain at the wafer center due to reduced centrifugal force at the center, as well as reduce the water spray-induced damage to low-density film coatings at the wafer center by spreading the impact energy of the spray across a larger surface area on the wafer.
The cleaning efficiency of the water jet 22 ejected from the nozzle 30 depends on various factors including the pressure and size of the water jet 22, as well as the scan density of the water jet 22 on the wafer 10. It is well-known that ejecting a water jet of high scan density onto the surface of a wafer effectively removes particles from the wafer. However, the scrubber cleaning cycle for each wafer is typically subjected to a timing limitation. This timing limitation, which is typically about 45 seconds, depends mainly on the size of the jet pump used to force the water through the nozzle adaptor 26 and out the single spray opening 32 of the nozzle 30.
Frequently, the typically 45-second scrubber cleaning cycle time of the wafer scrubbing apparatus is inadequate to sufficiently remove particles from a wafer. Thus, the wafer must be subjected to a second scrubber cleaning cycle time to remove the remaining particles from the wafer. However, this adversely affects wafer throughput. Accordingly, a jet clean nozzle having multiple openings is needed to increase the scan density of water jets on a wafer during a scrubber cleaning process and increase the wafer-cleaning efficiency during a scrubber cleaning cycle of typically limited duration.
An object of the present invention is to provide a novel jet clean nozzle having multiple openings.
Another object of the present invention is to provide a novel multi-aperture jet clean nozzle which is capable of increasing the scan density of water ejected against the surface of a wafer.
Still another object of the present invention is to provide a novel jet clean nozzle which enhances the wafer-cleaning efficiency of a scrubber cleaning apparatus.
Yet another object of the present invention is to provide a novel jet clean nozzle which is capable of contributing to an enhanced yield of IC devices fabricated on a semiconductor wafer.
A still further object of the present invention is to provide a novel jet clean nozzle which contributes to the thorough cleaning of a wafer surface within a scrubber clean cycle of limited duration.